Cellular radio networks are constantly evolving. The third generation partnership project (3GPP) is an organization setting standards for mobile communication. The standards are structured as releases. New functionality is entered into the standard as new releases are launched.
Third Generation Partnership Project (3GPP) network sharing architecture allows different core network operators to connect to a shared radio access network. In accordance with one supported architecture a radio access network (RAN) is shared and is referred as the Multi-Operator Core Network (MOCN) configuration.
As shown in FIG. 1, the architecture for Multiple Operator Core Network (MOCN) allow different core network operators to connect to a shared radio access network (RAN), see 3GPP Technical Specification TS 23.251 V10.5.0, “Network Sharing Architecture and functional description”, Technical specification group services and system aspects, December 2012. The operators do not only share the radio network elements, but also share the radio resource themselves. Each cell in shared RAN shall broadcast multiple Public Land Mobile Network (PLMN)-identities corresponding to multiple operators in system information. A User Equipment UE from any of a number of Operators such as Operator A, B or C can decode the broadcast system information and know that this is a cell that it can camp on. In accordance with this information the UE performs the cell (re)selection procedures in a conventional manner.
Public Land Mobile Network (PLMN)
Each public land mobile network (PLMN) operated by one particular operator is identified by a “PLMN identity”. For ease of understanding one can consider each PLMN identity as one operator in a simplified model. One or more PLMN identities shall be broadcasted in the system information, see 3GPP TS 36.304 V10.6.0, “User Equipment (UE) procedure in idle mode”, Technical specification group radio access network, June 2012.
It is very possible that one operator has dedicated RAN in which only its own PLMN identity is broadcast, and shared RAN in which its PLMN identity is broadcast along with other operator's PLMN identities. Each found PLMN shall be reported to the Non Access Stratum (NAS) for PLMN selection, see details in 3GPP TS23.122 V10.5.0, “Non-Access-Stratum (NAS) functions related to Mobile Station in idle mode”, September 2011.
Cell Selection/Reselection
The cell selection and reselection procedure is used so that a UE can camp on a cell. The detailed procedure is described in 3GPP TS 36.304 V10.6.0, “User Equipment (UE) procedure in idle mode”, Technical specification group radio access network, June 2012.
Random Access
When a UE camps on one cell in a RRC_IDLE state, random access is used for initial access when establishing a radio link, thereby switching from RRC_IDLE state to RRC_Connected state. The switch is triggered by any of the two following reasons:                Mobile originating: UE has originate services (delay-sensitive or delay-tolerant) for transmission to base station;        Mobile terminating: UE receives the paging information from base station.        
During the process of random access, the UE is attempting to access the camped cell whatever the type of access attempt is.
There is a constant desire to improve existing systems and to provide more efficient radio systems.